Compensating device for scales.



PATEN'I'ED DEC. 19, 1905.

J. H. SWIHART. GOMPENSATING DEVICE EUR SCALES.

APPLICATION FILED APR.14. 1902.

UNITED sTATEs PATENT oEEIoE.

COMPENSATING DEVICE FOR SCALES.

Specification of Letters Patent.

Patented Dec. 19, 1905.

Application filed April 14, 1902. Serial No. 102,737.

To all whom it may concern:

Beit known that I, JOHN H. SWIHAET, acitizen of the United States, residing at Elyria, in the county of Lorain and State of Ohio, have invented new and useful Improvements in Oompensating Devices for Scales, of which the following is a specification.

This invention relates in general to weighing devices, and has particular reference to the means employed for securing accurate indications or readings on spring-scales regardless of the variation of the temperature of the room in which the scale is placed.

As is well known, an increase of temperature expands or lengthens and weakens the springs in scales, thus making them more flexible, with the result that an object of a given weight will give a higher indication on such a scale than it would if the temperature were lower. Various means may be employed for effecting the necessary correction of readings automatically, some of which are shown in the accompanying drawings, in whichw Figure l represents the weighing parts of a spring-balance scale having one form of my compensating device applied thereto, the dial, the index-finger, and the front plate being removed to show the arrangement of the interior parts. Fig. 2 shows in side elevation a form of rack that I prefer to use with this form of device, said ligure indicating the rack expanded so as to increase the length of its pitch-line. Fig. 2a is a view similar to Fig. 2, showing the rack bent in the opposite direction, due to contraction of the'parts at a lower temperature. Fig. 3 is a front elevation of the rack shown in Fig. 2. Fig. 4 is a side elevation of this rack, showing the same at normal temperature. Fig. 4a is a transverse sectional view taken through Fig, 4 near the left end thereof. Figs. 5, 6, 6a, 7 8, and 8u illustrate other forms of racks that may be employed instead of that shown in Figs. 2 to 4, inclusive, Figs. 6n and 8u being sectional views taken through the racks shown in Figs. 6 and 8 near their smaller ends.

In view of the fact that the accuracy with which spring balance scales weigh varies with the temperature to which they are subjected it is customary for scale manufacturers to so adjust the springs and rack that the scales are likely to be subject in use. With a scale so adjusted, however, when the ternperature falls considerably below 7()O the effect of the cold is to give the springs greater resistance, either by shortening them or increasing their resisting' power. Conversely, when the temperature rises above I0O the springs are-\veakened in resisting power and A the scale gains in weight indication, so that a less weight of any substance will be required to indicate a given weight on the index or dial of the scale than would be required at TOO. In the drawings, in which similar reference characters designate corresponding parts throughout the several views, I have shown one form of device for compensating for these differences in the springs and for causing' the scales to give accurate indications regardless of the temperatures. Personally I regard 70C Fahrenheit as too high a temperature for the average, and I therefore adjust my scales at a temperature of 62O Fahrenheit.

In the drawings, l represents the casing of the scale, within which are the springs 2 2. To the lower end of these springs is secured the runner 3, to which is pivoted the lower end of the rack 4 and the upperend of the pendent bar 5, that carries the hook or other attaching means 6. The springs are preferably secured to the runner by inserting their lower ends through holes 77in the runner and then continuing them through slits 8 8 in the ends thereof, after which they are held by bending down those portions of the runner above the slits to make them grip the springs. Before carrying out this last operation, however, the scale is adjusted to Weigh accurately at the normal temperature, which adjustment rack is pivoted to the runner at a point directly below the shaft 11 and is held in mesh with the pinion by means of a spring 13, that engages with a shoulder 14 at the lower and rear' n strips 17 have expanded.

edge ofthe rack. A stationary pin or stud 15 also engages with the rear edge of the rack just back of the pinion to assist in holding these parts in mesh.

The racks 11 (shown in Figs. 1 to 1) are made of two metals having diferent coeiiicients of expansion and joined together in such a way that the entire rack warps with the changes in temperature. The back of the rack and the teeth are made oi' one piece of material, as shown at 16 in the sectional view of Fig. 1. Preferably this piece has a very low coefficient of expansion, and for this reason I use nickel-steel or nickel-iron, the expansibility of which is practically mil. The back of the rack is a lat plate that projects outwardly from the teeth, and on the `front of this back at each side of the teeth are secured strips of metal 17, that have a relatively high coellicient et' expansion. Vhile any suitable metal may be employed and while they may be secured to the back 16 in any suitable manner, I prefer to use zinc and to secure the strips by means ol' rivets placed close together, as shown. As will be noticed, the teeth of the rack are made of considerable length, andthe pitch-line is near their outer ends, so that when the rack warps, as shown in Fig.` 2, the pitch-line varies in length. On the left-hand side of that figure the pitch-line is lengthened, because the temperature has risen above 620 and the Zinc lonversely, on the right-hand side the pitch-line has shortened, because the temperature is below 620 and the zinc has contracted.

From this description it will be seen that when the springs 2 weaken with a rise in temperature the pitch-line lengthens correspondingly and that while the rack travels farther with a given weight it is longer at the pitchline and must needs travel Jfarther in order to give a correct reading. rIhus the changes in temperature cause the pitch-line of the rack to vary and compensate for the changes in rack travel dueto the variations of the spring, and the rack thus becomes a thermo-expansion regulator.

In the form of rack just described the teeth are cut in the least eXpansible metal-the nickel-steel or nickel-iron. In Figs. 5 and 6 I show a form in which the teeth are cut in the most eXpansible metal 18 and extend only part way to the backing 19, which consists of a plate oi' metal of a low coeliicient of eXpansion, such as nickel-steel. Preferably the part 18 is made of brass, and its thickness below the roots of the teeth is substantially equal to the thickness of the metal 19. This form of rack is not so sensitive as that iirst described, the brass not being so expansible as the Zinc.

In Figs. 7 and 8 I illustrate a still different form of rack, in which the strips 2O and 21 are preferably made of Zinc and nickel-steel, respectively, and are held together by the teeth 22, that are passed through the same and riveted, as shown. As these pin-teeth are separated and can be made of any length practicable, and the variation of the pitch-line dependsfupon the length of the teeth, the sensitiveness of the device can be materially increased ordiminished byemploying this form of rack and varying the length of teeth thereon.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is-

1. In a weighing device, a pinion, and a thermo-expansion rack for moving the pinion, the pitch-line of said rack varying with the changes in its ten'iperature, substantially as described.

2. In a thermo-expansion regulator, a pinion, a rack for turning said pinion, said rack being composed of a plurality oit pieces of different metals that are so associated together as to cause the pitch-line to be a straight line at one temperature, a convex line at a higher temperature, and a concave line at a lower temperature.

3. In a spring-scale, a pinion, a rack engaging with said pinion and being' composed of two layers of metal, the metal of each layer having a coeiiicient of thermo-expansion dilferent-ifrom that ot' the other metal, and having the teeth cut in one of the layers only.

4. In a spring-scale, a pinion, arack engaging with said pinion and being composed ol two layers of metal ol dilii'erent coeliicients of expansion secured together to'lormathermoexpansion bar, and having its teeth cut in the less expansible metal.

5. In a spring-scale, the combination with the springs, the runner connecting the same, and means for suspending substances for weighing from the runner, a pinion, and a rack-bar attached to the runner for turning the pinion,said rack-bar being composed of two layers or' metal of different eoeflicients of eX- pansion, the layers being secured together to form a thermo-expansion bar, and having' the teeth cut in one of the layers only.

6. In a spring-scale, a pinion, a rack engaging with said pinion and having the elongation or contraction of the pitch-line abnormally increased by forming the rack of two layers of metal of different eoeicients of expansion secured together and having the teeth cut in one of the metals only.

7. In a spring-scale, a pinion, a rack having the back and teeth composed of a metal having a low coeiiicientof thermo-expansion, and strips of Zinc secured to the back on opposite sides of the teeth.

8. In a spring-scale, the combination with the springs, the runner connecting the same, and means for suspending substances for weighing from the runner, a pinion, and a rack-bar attached to the runner for turning the pinion, said rack-bar having the back and IOO IIO

teeth composed of a metal having' a 10W ooof Zinc secured to the back on opposite sides efficient of thermo-expansion and strips of ofthe teeth, for the purpose speeied. IO Zinc secured to the back on opposite sides of In testimony Whereo` I axiny signature in the teeth. the presence of two Witnesses.

5 9. In aweighing device, apinion, and a rack JOHN H. SVVIHART.

for turning the pinion, said rack havingthe Witnesses: back and teeth composed of a metal having a S. E. FOUTS,

low coeieient of thermo-expansion, and strips l JAMES T. HARDING. 

